Sunday, January 27, 2013

ActiveE Torque Measurements

One of the most amazing things about driving an electric car is the instant torque. The ActiveE is fun to drive, but it is sometimes hard to compare against internal combustion engine cars. When my local chapter of the BMW Car Club of America recently held a Dyno Day, I was eager to put the ActiveE to an objective performance test. Dietsch Werks at Club Auto Sport just installed an in-ground AWD Chassis Dyno built by SuperFlow Technologies Group to measure torque and horsepower output. There were more than a dozen cars at the event, and of course someone scheduled the whisper-quiet electric car behind an M5 with an amazing exhaust note. Luckily, nobody was disappointed with the muted electric vehicle, especially after the torque numbers started showing up on the screen.

The ActiveE put up by far the largest torque numbers of the day, ahead of an X5M, M5, and plenty of other Porsche 911s and BMWs. We did runs with and without Eco Pro mode and the numbers came up to 490 pound feet of torque without eco pro mode, and over 460 pound feet of torque with it engaged. As expected for an EV, the torque curve shows maximum torque shortly after rest, however, the number is significantly higher than expected. The BMW ActiveE page notes that the electric motor puts out just 184 pound feet of torque, so I'm not sure what to make of the large discrepancy.

After the run, nearly every warning light on the car's dashboard was illuminated. As is often the case with the ActiveE, however, just giving it the old Microsoft Windows treatment of turning it off and back on again cleared everything.

I read your Blog and really like it!Thanks for the picture with the torque you posted. The numbers are quite high so I thoughd about them and I believe that I found an answer:On the posted image the x-Axis has [RPM] as a unit. The measure ends at 4200 RPM. So I think that here is the problem. The ActiveE Website says that the car has its highest torque of 184poundfeet from 0 RPM to 4450 RPM. After that the tourque falls on a dimishing scale. But the posted image does not match was BMW says. When you look on the picture above you see that the starting point where the decrease really takes place (it is a point of dicontinuity) ist not 4.450 RPM - it is around 1.700 RPM. But the RPM is needed to calculate the torque of the vehicle. In the picture above the shown RPMs do not fit the real RPMs of the engine. If you divide 4.450 by 1.700 you get a scaling factor of 2,62. If you divide your measured 490 pound feet tourque through the scaling factor of 2,62 you get (surprise): 187.2 pound feet of tourque. So your ActiveE is above the manufactor information - but not very much.I hope that what I wrote is understandable!

Have fun with your ActiveE - I drove it several times and agree that it is a fun car to drive!